“Sterilization” has been defined as the process of destroying all microorganisms, spores and their pathogenic products. A 6 log reduction in the amount of such pathogens is generally required to provide a suitable sterility assurance level. “Disinfection” is a similar process, the difference being that it results in a lesser degree of biocidal effect, particularly on bacterial spores. Disinfection is thus easier to achieve than sterilization.
The term “sterilant” will be used throughout although it is understood to encompass both “sterilant” and “disinfectant”.
Heat has traditionally been one option for carrying out sterilization. However, heat sterilization is not always practical, for example, when sterilizing heat-sensitive articles, such as certain medical instruments, or when sterilizing large areas, as in the case of room sterilization. For this reason, low-temperature sterilization is often the best option.
Low-temperature sterilants are usually liquids and can be applied to articles requiring disinfection or sterilization in a variety of ways. In recent years, the use gas or aerosol dispensing technologies to dispense sterilants has become widespread. Gas or aerosol processes are particularly attractive since they reduce the amount of liquid sterilant used. The primary benefit of using micro volumes of liquid is that rinsing steps can sometimes be eliminated and drying times are often significantly reduced compared to using say, soaking baths. This shortened cycle time reduces the turnaround time for any given instrument which in turn translates into a much smaller capital outlay tied up in instruments.
Gas or aerosol processes also tend to be conducted in closed systems, which means that operator safety is also enhanced relative to conventional methods that expose workers to large volumes of open sterilant solutions.
In recent years the use of hydrogen peroxide or peracetic acid as a sterilant has become greatly preferred. Hydrogen peroxide has been used in the vapour phase for disinfection or sterilization. Vapour phase systems generally employ small volume chambers such as sterilizers that can be evacuated since the vapours are more effective at very low pressures or as plasmas. At the end of the treatment cycle, residual hydrogen peroxide vapour is pumped out by a vacuum pump and exhausted to the atmosphere directly or via a catalytic destroyer which decomposes any residual peroxide vapour into harmless oxygen and water.
Peroxide vapours have also been used at atmospheric pressure but in that case longer treatment times are generally involved than in vacuum systems and efficacy against bacterial spores has been shown to be limited. After treatment in small scale peroxide vapour systems, air is circulated through the chamber and any residual peroxide is either flushed directly into the atmosphere through a HEPA-filter, or is flushed into the atmosphere via a catalytic destructor so that the peroxide is catalysed to oxygen and water prior to disposal. In some recirculating systems the flow may be diverted after the treatment and recirculated by an air pump though a catalytic destroyer placed in parallel with the treatment circuit until peroxide is eliminated.
Others have endeavoured to use peroxide aerosols (rather than vapour) as the biocidal agent for sterilization or disinfection of small chambers. Aerosols have a number of major advantages over vapour process. A much higher concentration density of active species is obtainable at atmospheric pressure for aerosols than for vapours. Aerosols also eliminate the need for costly vacuum equipment. In some such cases the aerosol flow may be diverted through a catalytic destructor after the treatment cycle is completed to remove any peroxide residues.
While such stable aerosols of aqueous biocides, preferably hydrogen peroxide, can be employed at atmospheric pressure and above which avoid the need for vacuum equipment, elimination of residual hydrogen peroxide on the surface of sterilized articles nevertheless remains a significant problem.
In the food sterilization field, even trace amounts of hydrogen peroxide can affect the flavour or colour of the product. Food packaging regulations now limit hydrogen peroxide residues on containers to a maximum of 0.5 ppm in the United States.
In the case of medical instruments, even a small amount of residual peroxide on an ultrasound probe or similar could have potentially serious consequences for a patient if the probe were to be placed in direct contact with the patient's skin or mucosa. Peroxide in high concentrations is highly corrosive and can result in severe wounding. For similar reasons, the use of peroxide as a sterilant means that occupational health and safety measures need to be in place to ensure the safety of staff working in disinfected environments.
Surface residues of peroxides in operating theaters or on surgical instruments should be below 100 mkg/cm2. To achieve such levels by blowing or sucking air even though small chamber volumes for sterilizing instruments or the like can add significantly to process times, especially when the incoming air needs also to be HEPA-filtered to maintain sterility. The removal step thus adds greatly to treatment times because the residual balance of peroxide reduces asymptotically. The larger the volume of space treated the more difficult the removal problem becomes.
Similar considerations apply to biocides other than peroxides.
In addition, it is not feasible to check every sterilization cycle of every apparatus or every room or space treated in order to ensure complete sterilization. Certification of sterilant removal, i.e. guaranteed removal of the sterilant or reduction of the sterilant to a certain level is highly desirable. Following the stated protocol as a way to achieve a guaranteed or certified outcome is very efficient mode of operation. However, it can still be highly desirable to perform a quick test to confirm experimentally whether a guaranteed level of certification of sterilant removal is actually achieved. Ideally, such a test would be “on/off” or ‘go/no-go”, meaning that the when the test is conducted, a clear answer would be given as to whether a certain level of residual was present or not.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.